Repairing cast under bathroom sink??
Cast has HUGE bells where it is oakemed and 'leaded' together,,,is THAT what you are seeing?? Usually cst doesnt rust thru too much,,,was it galvanized iron pipe attached to the cast?? They make a doughnut,called a fernco doughnut, BUT there are alot of different sizes for same size pipe,,,ie light cast,medium cast,,,and extra heavy cast if you see a couple of (X's) on cast bell,its probably extra heavy cast. To use those you have to 'dig' all that lead out of the joint,,,careful you dont break next piece,the bell ...A drill screwdrivers and alot of different tools to remove it and it takesTIME. they ARE stubbon. when you get down to the oakem your home free. Dont know HOW well a hand torch might melt lead out,never tried that but be careful of cobweb and wall fires,,I always did it the hard way with a drill and screwdriver ,,,again VERY CAREFULLY. you can make a HUGE project out of a little one VERY quickly!! Make sure that doughnut goes in there HARD. GOOD LUCK,you may need it,,,if I am wrong in interpeting your question,try again!!